In order to obtain the maximum speed of a sailboat for any particular wind or sea condition, it is necessary to position with accuracy the boom which controls the shape and the orientation of the mainsail.
For this purpose, the mainsheet tackle which connects the boom with the boat is attached at its lower extremity to a traveler car which is movable along a trackway mounted transversally across the boat. This traveler car is fitted with two tackles one on each side, their extremities being respectively fastened to the car and to the trackway ends.
At a given moment, only one tackle has to be manoeuvered, it is the tackle which counterbalances the force of the wind transmitted to it, via the sail, the mainsheet and the car.
Once the right position has been found, the control rope of this tackle has to be secured, generally in a cam cleat of conventional design which can be mounted either on the car or at trackway ends.
With such a system of opposing tackles, if you want to tack from star to portboard, you must first release the starside traveler control line, move to the portside of the boat to operate the portboard tackle and secure it.
This is a tricky operation at a moment when heel changes from side, when boom swings over the crewmen's heads and when the crew has to sit on the other side of the boat to counterbalance by its weight the new heel.
It is still more difficult with only one man on board who has to finely control the tiller at that moment and who is eventually holding the main sheet.
To our knowledge, several solutions to the problem of manoeuvering the cleats from the sole windward side have been proposed, with the cleats only fitted on the traveler car and not at trackway ends. Several ways have been explored.
The U.S. Pat. No. 4,147,121 is based upon the principle of a sliding cleat opener: a sliding part of the traveler car on which are mounted the cleats and the end pulleys of the tackles is moved by the relative force existing between the mainsheet and the windward tackle. The jaws of the leeside cleat are then pushed against a finger fastened in fixed relation to the traveler and automatically opened.
This patent is extended to any solution using means to open a cam cleat by a physical contact with the cams. It is based on the "cleat opener" principle.
The German patent 30 44 492A is based upon the principle of a rocking structure pivoting in the middle of the traveler car with its axis transversal to the track, the ends of said structure being engaged under the falls of the two tackles between the tackle pulleys and the cam cleats, in such a manner that if by example, the fall is tightened from the portboard side, it lowers the portboard end of the structure and can be inserted in the cleat, whereas the starboard side of the structure has pivoted well above the starboard cam cleat, preventing the starboard fall to be cleated and having eventually pushed it out of the cleat. It is a "rope lifter" principle.
Both ways have the disadvantage that, by inherent design, only one fall is cleated at a time, the windward one, and this can be dangerous when sailing off the wind. At this course, the direction of wind can suddenly change, throwing the traveler car against its stop without limiting the boom swing.
A second disadvantage is the inability to easily use these principles when the stoppers are to be mounted at track ends.
A third disadvantage is that these designs are not very flexible and need several models to cover a range of cars generally different by only their length; moreover, they are not able to cover easily a combination of two or several cars, often used for curved tracks or to increase the working load.
It is therefore clearly desirable to have a safer and more flexible system for automatic stoppers.